1. Field of the Invention
This invention relates generally to scrubbing of effluent gases and more particularly to scrubbing of gases that are not water soluble.
2. Description of the Prior Art
Various gases, some toxic and some highly corrosive or reactive, are used in semiconductor manufacturing processes. Scrubbers are used for cleansing any mixture of gases that remains at the conclusion of a manufacturing procedure. Most such scrubbers operate by passing the mixture of gases through a mist of a fluid such as water; these scrubbers are known as wet fume scrubbers. Some gases, of which a few examples are chlorine, fluorine and ammonia, are water soluble and are readily removed by this method. Other gases such as silane (SiH4), arsine (AsH3), phosphine (PH3), and germane (GeH4) are not water soluble. A shortcoming of wet fume scrubbers has been their inability to remove gases such as silane that are not water soluble.
Many water-insoluble gases are oxidizable and in principle can be disposed of with the assistance of an oxidizing agent such as oxygen. Various systems and methods based on the use of an oxidizing agent to remove water-insoluble gases have been proposed. Among these are U.S. Pat. No. 5,271,908 issued to Shiban et al. on Dec. 21, 1993, U.S. Pat. No. 6,084,148 issued to Shiban et al. on Jul. 4, 2000, U.S. patent application Ser. No. 09/957,424 filed Sep. 21, 2001 by Tong et al. and published Mar. 27, 2003 as Publication No. 2003/0057576, U.S. patent application Ser. No. 10/849,435 filed May 19, 2004 by Arno et al. and published Oct. 28, 2004 as Publication No. 2004/0213721, U.S. patent application Ser. No. 11/217,780 filed Sep. 1, 2005 by Tong et al. and published Jan. 5, 2006 as Publication No. 2005/0002380.
A 1998 German report bearing the identifier Forderkennzeichen 254 116 98 and titled “Verfahrensentwicklung zur Herstellung von Solar-Silicium im halbtechnischen” also addresses the problem. This last reference reports on a laboratory test of a benchtop replication of a scrubber. The test reported on the reaction of silane with sodium hydroxide or potassium hydroxide. Sodium hypochlorite was also added as an oxidation agent but showed no influence on the silane conversion. The report noted that small flames were observed in those experiments that employed sodium hypochlorite due to gas bubbles on the liquid surface. The report concluded, with respect to the use of sodium hypochlorite that adding sodium hypochlorite is dangerous because of the intense reaction with silane. Accordingly, there remains a need for a safe and economical way to scrub gases that are not water soluble from an effluent gas mixture.